The growing health consciousness and an aging population have increased the demand for home medical devices. However, usability issues are on the rise, especially for the elderly. This study aims to develop design guidelines for home medical devices used by the older adults through multidimensional usability testing. Taking oxygen concentrators as an example, the research involves desk research to identify target user characteristics, empirical research with eye-trackers, and semi-structured interview. The study analyzes the limitations of elderly users in sensory, cognitive, physical capabilities, and usage environment. Based on user behavior findings, design optimization suggestions are provided. In conclusion, the study proposes design improvement suggestions to help designers (often younger) to gain insight into older adults, as well as design reference.